Unless either of you object to killing courageous enemies, I’m not sure their courage is relevant.
The definition is very relevant, since it gives sanction to the act.
Pearl Harbor was always considered a cowardly act since it was done while the Japanese were still negotiating with us.
Attacking unarmed civilians, who are not even aware they are in a war, is a cowardly act, not a courageous one, as Bill Maher, tried to define it.
I think that an enemy's courage plays no part in whether I should kill him or not. An enemy's level of courage is relevant, however, in determining tactics to employ to meet one's strategic goals while fighting him. If I were, for example, to simply consider my opponent cowardly, I might believe he is likely to surrender at the threat of his life...and conduct myself in a restrained manner, hoping for acquiescence.
However, if I recognize that my opponent is willing to risk or sacrifice his life for his cause, then I can have appropriate expectations (no surrender) and take an appropriate response (defense against unconventional tactics).
Although my opponent's intentions, honor, morality, etc., might have no bearing on deciding whether to fight, his courage does. And we must learn to stop misunderestimating (sic) our foes just because it makes us feel good to put them down or to comment on their moral failures.